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Basics of CSF Diversion

Relieving intracranial hypertension – by lowering intracranial pressure – via permanent CSF diversion is regarded as an effective treatment option for this group of patients.  

The evaluation, diagnosis and management of IIH patients is complex and requires not only input from primary care physicians and neurologists, but also includes ophthalmologists, neurosurgeons, and interventional neuroradiologists who must work in concert to appropriately treat this illness.

A minority of patients either present with fulminant IIH symptoms or fail medical management, requiring procedural intervention to preserve vision and improve symptoms.  Relieving intracranial hypertension – by lowering intracranial pressure – via permanent CSF diversion is regarded as an effective treatment option for this group of patients.  

The Basics of CSF Diversion

CSF diversion is commonly known as shunting or a shunt, quite simply refers to the placement of a permanently implanted tube that diverts CSF to another area of the body where it can be reabsorbed.  This surgery is performed by neurosurgeons, occasionally with the assistance of other surgical specialists depending on the type of shunt (more on that below). The ‘proximal’ portion or beginning of the shunt is that end of the tube that lies within the CSF space.  The tube then traverses subcutaneously where its ‘distal’ end is placed within the body cavity where the CSF is ultimately diverted to for reabsorption.  

Frequently, there are valves or other devices that lie along the path of the tube that can regulate the amount of CSF that is drained.  With regards to the valves themselves, two general varieties include programmable and non-programmable valves.  Non-programmable valves drain CSF when the intracranial pressure is above a certain level – and this level is determined by the valve itself and cannot be changed.  Programmable valves allow the intracranial pressure at which CSF will drain to be adjusted by the neurosurgeon.  The adjustment itself is noninvasive, utilizing a small handheld magnet, and is done in a clinic setting. Furthermore, there are other devices, known as anti-siphon devices, that prevent overdrainage of CSF based on patient position.  These devices may be built into a valve or be placed in series along the path of the shunt tubing.

Shunt procedures are frequently defined by preceding terminology that defines the location of the ‘proximal’ portion or beginning of the tube followed by the ‘distal’ portion or end of the tube.  The most common type of shunt procedure is the ventriculoperitoneal shunt, frequently abbreviated as a VP shunt.  ‘Ventriculo-” refers to the location of the proximal tube portion being located within the ‘ventricles’ of the brain – the fluid spaces within the brain proper where CSF is made daily.  ‘-peritoneal’ refers to the distal tube portion’s location within the ‘peritoneal cavity’, a space within the abdomen where many internal organs, such as the intestines and liver, reside.  

With this understanding of the nomenclature, it becomes easy to decipher the other types of shunts that are commonly performed by neurosurgeons:

  • Ventriculopleural shunt: drains CSF from ventricles within brain to pleural cavity in chest where the lungs are located
  • Ventriculoatrial shunt: drains CSF from ventricles of the brain to large veins returning venous blood to the heart (‘atrium’)
  • Lumboperitoneal shunt: drains CSF from the lumbar cistern in the lower back to the peritoneal cavity

Common questions regarding shunts can reveal misconceptions among patients and referring physicians that can be easily answered. 

Benefits and Risks of Shunt Procedures

As mentioned above, shunts are performed to preserve visual function and ameliorate the other symptoms of IIH, including headache.  To learn more about the efficacy of shunts for IIH compared to other procedures, click here.

Risks of shunts include infection and malfunction of the shunt.  These complications can lead to the need for further surgery to remove or revise the shunt.  Additionally, overdrainage of CSF (mentioned above) can be a disabling symptom of low intracranial pressure which may necessitate further surgery to correct.

Misconceptions Regarding Shunts

Common questions regarding shunts can reveal misconceptions among patients and referring physicians that can be easily answered.  These include:

Can a patient have an MRI after a shunt?

The short answer is yes.  Shunts placed currently are compatible with MRI, which is important as MRI is occasionally used in the management of IIH patients as well as other medical conditions.  Programmable valves also utilize small ferromagnetic components in their design, and while there isn’t a risk of harm, there is a risk that the valve setting could change during the MRI. For this reason, patients with programmable valve shunts having MRIs should follow up with their neurosurgeon the same day to ensure the correct valve setting.

Is a shunt for IIH permanent?

Shunts placed for CSF diversion are permanent implants, in the sense that they are not removed for any other reasons than 1) infection or 2) they cease working in a patient who continues to require a shunt.

Ventriculoperitoneal vs. Lumboperitoneal Shunting

The two most common types of shunts for IIH patients are ventriculoperitoneal (VP) or lumboperitoneal (LP) shunts.  Traditionally, LP shunts were favored in IIH patients as the small ventricular size (so-called ‘slit ventricles’) made placement within the ventricle more difficult.  However, a 2014 study by Menger at al. found LP shunts associated with an increased need for shunt revision, length of stay, and costs to the healthcare system. (Menger RP, Connor DE Jr, Thakur JD, Sonig A, Smith E, Guthikonda B, Nanda A. A comparison of lumboperitoneal and ventriculoperitoneal shunting for idiopathic intracranial hypertension: an analysis of economic impact and complications using the Nationwide Inpatient Sample. Neurosurg Focus. 2014 Nov;37(5):E4. doi: 10.3171/2014.8.FOCUS14436. PMID: 25363432.)  In certain centers, this has caused a shift towards VP shunts, often utilizing stereotactic navigation to guide placement within the ventricle.  There are specific benefits and risks to both procedures, and the decision regarding which procedure is best is determined by the treating neurosurgeon.

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